Various sensors are known in the magnetic effect sensing arts. Examples of common magnetic effect sensors include Hall effect sensors, differential Hall sensors, and magnetoresistive sensor technologies. Such magnetic sensors can respond to the change of magnetic field as influenced by the presence or absence of a ferromagnetic target object of a designed shape passing by the sensory field of the magnetic effect sensor. The sensor can then provide an electrical output signal, which can be further modified as necessary by subsequent electronics to yield appropriate sensing and control information thereof. Associated electronics may be either onboard or outboard of the sensor package.
Geartooth sensors, for example, are known in the automotive arts to provide information to an engine controller for efficient operation of the internal combustion engine. One such known arrangement involves the placing of a ferrous target wheel on the crankshaft of the engine with the sensor located proximate thereto. The target objects, or features, i.e., tooth and slot, are, of course, properly keyed to mechanical operation of engine components. Such sensors can be configured according to the Hall effect, which is well known in the magnetic sensor arts.
The Hall effect has been known for many years. Hall effect sensors are typically based on the utilization of a Hall generator, which generally comprises a magnetic field dependent semiconductor whose function rests on the effect discovered by Edwin Hall. This effect, known as the “Hall effect,” is caused by the Lorentz force, which acts on moving charge carriers in a magnetic field.
One of the first practical applications of the Hall effect was as a microwave power sensor in the 1950s. With the later development of the semiconductor industry and its increased ability for mass production, it became feasible to use Hall effect components in high volume products. In 1968, Honeywell International Inc., for example, has produced a number of solid-state sensor devices that take advantage of the Hall effect. The Hall effect sensing element and its associated electronic circuit are often combined in a single integrated circuit.
In its simplest form, a Hall element can be constructed from a thin sheet of conductive material with output connections perpendicular to the direction of electrical current flow. When subjected to a magnetic field, the Hall effect element responds with an output voltage that is proportional to the magnetic field strength. The combination of a Hall effect element in association with its associated signal conditioning and amplifying electronics is sometimes called a Hall effect transducer.
In the differential Hall sensor, two Hall generators may be arranged close to one another. The individual Hall generators operate along the same principle as the magnetic dependent semiconductor in single Hall effect sensors. Both Hall elements are generally biased with a permanent magnet.
Transmission manufacturers generally desire a single sensor to sense the speed and direction of a transmission mechanism. Comparing two output signals and determining which output signal leads or lags the other, with a desired phase between the two signals of approximately 90 degrees, can obtain direction information. Speed information can be obtained by monitoring an associated pulse width or period width of one of the output signals.
In some angle position sensing applications, a Hall-based angle position sensor design can be implemented, utilizing a single Hall effect sensing element to provide one output signal that is proportional to rotation. In such a configuration, the optimum location of the Hall effect sensing element is based on an alignment of the centerline of the sensing plane with the centerline of an associated magnetic bias circuit, which can also be referred to as the “bias magnet.” The Hall effect sensing element senses the absolute magnitude of the magnetic field generated by the bias magnet. A low temperature coefficient (TC) material is ordinarily utilized for the bias magnet to minimize the temperature effects of the absolute magnetic field generated by the bias magnet and many readily available Linear Hall effect IC's also provide the provision of compensating for the nominal TC of the bias magnet. In the single Hall element sensing configuration, if the Hall effect sensing element is misaligned from the centerline of the rotational axis of the bias magnet, a significant reduction in sensing accuracy typically results because the Hall effect sensing element no longer senses the “sweet spot” of the bias magnet.
In some applications where the sensors output is related to a safety critical function, it may be necessary to design and incorporate the use of a redundant output. A number of such prior art systems have been implemented, and the two most typical output configurations have one output signal inverted from the other to create an X. Another common configuration involves one output having one half the sensitivity of the other signal. In this regard, additional information can be gained by comparing the two output signals and can indicate system failures or potential wire fault detection methods. When two Hall elements are utilized, however, it is no longer possible to simultaneously align the centerline of the sensing plane of both Hall elements with the centerline of the rotational axis of the bias magnet.
The ideal location of the centerline of the sensing plane of each Hall element is to be as close as possible to the centerline of the rotational axis of the bias magnet. Another method involves minimizing the effects of placement tolerances and misposition, and increasing the size of the bias magnet to increase the area of the “sweet spot” of the bias magnet. Increasing the magnet size, however, increases the cost of the overall magnetic sensing system. It is therefore believed that an improved magnetoresistive sensing system is required to overcome these problems. Such a system and methodology are disclosed in greater detail herein and helps to minimize the distance between the sensing plane of each Hall element to the centerline of the rotational axis of the bias magnet